1. Field of the Invention
The present invention relates generally to processes for filtering solid impurities from oil, and more particularly, but not by way of limitation, to processes for purifying used lubricating oil to obtain an intermediate low-ash oil or a high-grade lube oil stock.
2. Description of the Prior Art
Due to the amount of compounds being added to lubricating oil to increase the performance thereof and due to the nature of most used lubricating oil available for re-refining, processes for re-refining or reclaiming used lubricating oil have become more complex.
Many compounds such as detergents, pour point depressants, oxidation inhibitors and viscosity index improvers are now added to lubricating oil to increase the performance thereof. For example, detergents are often added to suspend resins, carbon, dirt, wear metal particles and other impurities in the oil so that the impurities will remain with the oil when the oil is changed. Unfortunately, the additive compounds can be very difficult to remove from the oil after it is used.
Due to the fact that most service stations place all crank case drainings into a common tank, most used lubricating oil available for reclaiming processes is a blend of used lubricating oil from both gasoline and diesel engines. Waste oil containing a significant concentration of oil drained from diesel engines is more difficult to reclaim than that without, most likely because of the high level of carbon and/or soot particles present in used oil from diesel engines. The presence of various dispersants found in lubricating oil often hinders the agglomeration of such particles.
Various processes have been developed to remove additives and foreign particles from used lubricating oil. In many of these processes, the used oil is admixed with a treating agent which reacts with ash-forming contaminants in the oil to form a precipitate of reacted contaminants. The treated oil is then subject to filtration to remove the precipitate of reacted contaminants from the oil. Certain compounds can be added to the reaction mixture to facilitate the filtration step.
By the present invention, an improved process for facilitating filtration of used lubricating oil is provided.